The present invention relates to a primary containment vessel particularly of a boiling water reactor.
In conventional boiling water reactors (BWR), an advanced boiling water reactor (ABWR) has been well known as a latest reactor. A reinforced concrete primary containment vessel (RCCV) of the ABWR will be described below with reference to the accompanying drawings.
FIG. 15 is a schematically sectional view showing a conventional ABWR. As shown in FIG. 15, a primary containment vessel 1 is provided with a reactor pressure vessel 4 which is supported on a support skirt portion 3 by means of a substantially hollow cylindrical reactor pressure vessel (RPV) pedestal 2 at the middle portion in the primary containment vessel. An outer peripheral side of the reactor pressure vessel 4 is surrounded with a hollow cylindrical outer peripheral concrete wall 5. Each lower end portion of the outer peripheral concrete wall 5 and the RPV pedestal 2 is supported on a mat concrete wall 6. The outer peripheral concrete wall 5 and the RPV pedestal 2 are joined together by means of a horizontal wall 7 at the substantially central position in a vertical direction in an illustrated state of the RPV pedestal 2.
In the reactor pressure vessel 4, an upper side from the support skirt portion 3 is surrounded by an upper dry well 8 which is a space defined (surrounded) by the outer peripheral concrete wall 5, the horizontal wall 7 and the RPV pedestal 2. On the other hand, in the reactor pressure vessel 4, a lower side from the support skirt portion 3 is surrounded with a lower dry well 9 which is a space defined (surrounded) by the mat concrete wall 6 and the RPV pedestal 2. The lower dry well 9 includes a reactor water recirculation pump and a control rod drive mechanism, which are not shown. Further, the lower dry well 9 is provided with a wet well 10 which is a space surrounded by the outer peripheral concrete wall 5, the mat concrete wall 6, the horizontal wall 7 and the RPV pedestal 2, at the outer peripheral side thereof. The wet well 10 is provided with a suppression pool or chamber 11 in which water is stored, at a half of the lower side.
The RPV pedestal 2 is provided with a communicating hole 12. The communicating hole 12 functions as a gas passageway between the upper dry well 8 and the lower dry well 9, and extends from the lower dry well 9 so as to communicate a heat exchanger cooling pipe of a reactor water recirculation pump, an electric cable of the control rod drive mechanism, an air conditioning duct, which are included in the lower dry well 9 and are not shown, with the upper dry well 8. These pipe, electric cable duct and the like are connected to the outside of the primary containment vessel via a penetration member (not shown) from the upper dry well 8.
Further, the RPV pedestal 2 is provided with a vertical vent pipe 13, which is opened to the lower dry well 9 side, at a half portion on the lower side thereof. The vertical vent pipe 13 is connected to a plurality of horizontal vent pipes 14 at the lower end side thereof. These horizontal vent pipes 14 are opened to water of the suppression pool 11. The suppression pool 11 is stored with water capable of safely absorbing a thermal energy radiated from the reactor pressure vessel 4 when an assumed accident such as a main steam pipe breakdown accident happens.
The primary containment vessel 1 is provided with a passageway which penetrates through the outer peripheral concrete wall 5, the wet well 10 and the RPV pedestal 2, and communicates the outside of the primary containment vessel 1 with the lower dry well 9. The passageway includes an equipment carrying in and out passageway 15 for carrying in and out equipments included in the lower dry well 9, and a personnel passageway 16 for workers for coming in the lower dry well 9 from the outside of the primary containment vessel 1 so that the workers (personnel) do work in the lower dry well 9. These equipment carrying in and out passageway 15 and personnel passageway 16 are provided with a scram pipe of the control rod drive mechanism (not shown) from the lower dry well 9.
FIG. 16 is a cross sectional view taken along the line XVI--XVI of FIG. 15. As shown in FIG. 16, the primary containment vessel 1 is provided with the upper dry well 8 inside the outer peripheral concrete wall 5 having an ring shape in its cross section. The upper dry well 8 becomes a state of being filled with an inert gas such as nitrogen in order to prevent an explosion of a fuel assembly when a main steam pipe breakdown accident or the like happens. An inner peripheral side of the outer peripheral concrete wall 5 is provided with the RPV pedestal 2 which is surrounded by the upper dry well 8 and has a ring shape in its cross section. Ten (10), in total, communicating holes 12 are formed along the outer periphery of the RPV pedestal 2.
FIG. 17 is a cross sectional view taken along the line XVII--XVII of FIG. 15. As shown in FIG. 17, the primary containment vessel 1 is provided with the wet well 10 inside the outer peripheral concrete wall 5 having an ring shape in its cross section. An inner peripheral side of the outer peripheral concrete wall 5 is provided with the RPV pedestal 2 which is surrounded by the wet well 10 and has a ring shape in its cross section. The RPV pedestal 2 is formed with the totaled ten (10) vertical vent pipes 13 having a circular shape in a cross section thereof. The lower dry well 9 is formed inside of the RPV pedestal 2.
Further, the primary containment vessel 1 is provided with an equipment carrying in and out passageway 15 which communicates with the outside of the primary containment vessel 1 and the lower dry well 9 and carries in and out equipments included in the lower dry well 9, and a personnel passageway 16 which is a passageway for coming in the lower dry well 9 so that the workers do work in the lower dry well 9.
In the conventional primary containment vessel constructed as described above, in the case where an accident such as a main pipe breakdown accident happens in the upper dry well 8, the upper dry well 8 and the lower dry well 9 communicate with each other, and for this reason, a steam pressure of the upper dry well 8 and the lower dry well 9 rises up. Then, when the steam pressure becomes a predetermined pressure or more, a high pressure steam is jetted into the water stored in the suppression pool 11 via the vertical vent pipe 13 communicating with the lower dry well 9 and the horizontal vent pipes 14. The jetted high pressure steam is condensed by the water stored in the suppression pool 11, so that an atmospheric pressure of the upper dry well 8 and the lower dry well 9 can be reduced.
Moreover, in the case where an accident such as a small-diameter pipe breakdown accident happens in the lower dry well 9, the upper dry well 8 and the lower dry well 9 communicate with each other. Because of this reason, a steam pressure of the upper dry well 8 and the lower dry well 9 rises up. Then, when the steam pressure becomes a predetermined pressure or more, a high pressure steam is jetted into the water stored in the suppression pool 11 via the vertical vent pipe 13 communicating with the lower dry well 9 and the horizontal vent pipes 14. The jetted high pressure steam is condensed by the water stored in the suppression pool 11, so that an atmospheric pressure of the upper dry well 8 and the lower dry well 9 can be reduced.
An inner-diameter dimension of the primary containment vessel 1 is determined in view of an outer diameter of the reactor pressure vessel 4, an arrangement space of a main steam pipe isolation valve (not shown) connecting to the reactor pressure vessel 4, etc.
Further, a height dimension of the reactor container 1 is determined in view of a height dimension of the reactor pressure vessel 4, a control rod drive mechanism (not shown) located on the bottom portion of the reactor pressure vessel 4, a height dimension of a platform for maintenance and inspection of the control rod drive mechanism or the like.
The inner diameter and height dimensions thus determined need to satisfy a design pressure of the reactor container 1 in the case where an assumed accident such as a main steam pipe breakdown accident happens.
Taking the above assumed accident into consideration, the primary containment vessel 1 is divided into a part of the sum of the upper dry well 8 and the lower dry well 9 and a part of the wet well 10, and a pressure analysis is carried out using a sum of a free space volume of the upper dry well 8 excluding a volume of built-in pipe and equipments and a free space volume of the lower dry well 9 and a free space volume of the wet well 10 as one condition of the analysis.
In the case of the conventional primary containment vessel of the ABWR in the range of 1350 MWe, an error or the like on the analysis is 15% with respect to a design pressure 3.16 kg/cm.sup.2 g, and therefore, this is a value satisfying the design pressure. In this case, a ratio of a free space volume of the wet well 10 to the sum of a free space volume of the upper dry well 8 and a free space volume of the lower dry well 9 is about 0.81.
However, in the case where there has been made a request to increase an electric output from the conventional range of 1350 MWe, an outer dimension and a height dimension of the reactor pressure vessel 4 are made large together with an increase of a reactor core fuel (not shown). Because of this reason, a dimension of the inner diameter and height of the primary containment vessel 1 is increased.
With an increase of the electric output, there is a need of increasing the free space volume of the upper dry well 8 and the lower dry well 9, and therefore, in proportional to the increase of the free space volume of these dry wells, the free space volume of the wet well 10 also must be increased. As a result, a dimension of an inner diameter and height of the primary containment vessel 1 is increased.
Moreover, a reactor core fuel is increased in proportional to an increase of the electric output of the reactor pressure vessel 4, and therefore, a heating value held by the reactor pressure vessel 4 is also increased. For this reason, a quantity of water stored in the suppression pool 11 is also increased in proportional substantially to an increase of the electric output. Thus, in order to keep the quantity of water, the dimension of the inner diameter and height of the primary containment vessel 1 must be increased.